Process and arrangement for an air conditioner control with an evaporator protected against icing

Abstract

A process and an arrangement for controlling an air conditioner utilize an evaporator protected against icing and a refrigerant circulating system which includes at least one compressor and the evaporator. The evaporator temperature is sensed continuously and the compressor is deactivated when the evaporator temperature falls below a defined switch-off temperature. The compressor is activated again when the evaporator temperature exceeds a defined switch-on temperature which is at least equal to the switch-off temperature. The evaporator temperature gradient is determined by a corresponding control unit from the continuous sensing of the evaporator temperature. The switch-off temperature is variably defined as a function of the determined temperature gradient and is selected so as to rise with a negative evaporator temperature gradient, having an amount which increases, during operating phases with an activated compressor and/or with a falling positive evaporator temperature gradient during operating phases with a deactivated compressor.

What is claimed is: 
     
       1. Process for controlling an air conditioner with an evaporator protected against icing and a refrigerant circulating system which includes a compressor and an evaporator, comprising the steps of: continually sensing an evaporator temperature,   deactivating the compressor when the evaporator temperature falls below a defined switch-off temperature,   activating the compressor again when the evaporator temperature exceeds a defined switch-on temperature which is higher than or equal to the switch-off temperature,   determining an evaporator temperature gradient from continuously sensing the evaporator temperature during operating phases with a deactivated compressor and/or an activated compressor, and   variably defining the switch-off temperature as a function of the evaporator temperature gradient determined so that the switch-off temperature is selected to rise with a falling negative evaporator temperature gradient during operating phases with an activated compressor and/or with a falling positive evaporator temperature gradient during operating phases with a deactivated compressor.   
     
     
       2. Process according to claim 1, and further comprising the steps of defining a hysteresis distance of the switch-on temperature from the switch-off temperature to be variable as a function of the evaporator temperature gradient determined, and selecting the hysteresis distance so as to rise with a negative evaporator temperature gradient, with an amount which increases, during operating phases with an activated compressor and/or with a falling positive evaporator temperature gradient during operating phases with a deactivated compressor.   
     
     
       3. Arrangement for controlling an air conditioner with an evaporator protected against icing and a refrigerant circulating system which includes a compressor and an evaporator, comprising: an evaporator temperature sensor, and   a control unit to which evaporator temperature information is supplied by the evaporator temperature sensor, which deactivates the compressor when the evaporator temperature falls below a defined switch-off temperature, and which activates the compressor again when the evaporator temperature exceeds a switch-on temperature which is at least equal to the switch-off temperature,   wherein the control unit determines, from the continuously supplied evaporator temperature information, an evaporator temperature gradient during operating phases with a deactivated and/or activated compressor and variably defines the switch-off temperature as a function of the evaporator temperature gradient determined, said switch-off temperature rising with a falling negative evaporator temperature gradient during operating phases with an activated compressor and/or with a falling positive evaporator temperature gradient during operating phases with a deactivated compressor.   
     
     
       4. A control arrangement for an air conditioner including a refrigerant cooling system having a compressor and an evaporator, said control arrangement comprising: a sensor which detects an evaporator temperature, and   a control unit which determines an evaporator temperature gradient, deactivates the compressor when the evaporator temperature falls below a switch-off temperature to protect the evaporator against icing and activates the compressor again, after deactivation when the evaporator temperature falls below the switch-off temperature, when the evaporator temperature exceeds a switch-on temperature at least equal to the switch-off temperature,   wherein said switch-off temperature is set as a function of the evaporator temperature gradient.   
     
     
       5. A control arrangement according to claim 4, wherein the control unit sets the switch-off temperature higher when the evaporator temperature gradient is low and positive. 
     
     
       6. A control arrangement according to claim 4, wherein the control unit sets the switch-off temperature higher when the evaporator temperature gradient is high and negative. 
     
     
       7. A control arrangement according to claim 4, wherein said control unit determines a switch-on hysteresis as a function of said evaporator temperature gradient. 
     
     
       8. A control arrangement according to claim 7, wherein said switch-on hysteresis gets larger as the evaporator temperature gradient gets lower when said compressor is deactivated and said gradient is positive. 
     
     
       9. A control arrangement according to claim 7, wherein said switch-on hysteresis gets larger as the evaporator temperature gradient gets larger when said compressor is activated and said gradient is negative. 
     
     
       10. A control process for an air conditioner including a refrigerant cooling system having a compressor and an evaporator, said control method comprising the steps of: detecting an evaporator temperature,   determining an evaporator temperature gradient,   deactivating the compressor when the evaporator temperature falls below a switch-off temperature to protect the evaporator against icing and activating the compressor again, after deactivation when the evaporator temperature falls below the switch-off temperature, when the evaporator temperature exceeds a switch-on temperature at least equal to the switch-off temperature, and   setting said switch-off temperature as a function of the evaporator temperature gradient.   
     
     
       11. A control process according to claim 10, wherein the switch-off temperature is set higher with decreasing positive evaporator temperature gradient. 
     
     
       12. A control process according to claim 10, wherein the switch-off temperature is set higher with falling negative evaporator temperature gradient. 
     
     
       13. A control process according to claim 10, wherein a switch-on hysteresis is defined as a function of said evaporator temperature gradient. 
     
     
       14. A control arrangement according to claim 13, wherein said switch-on hysteresis gets larger as the evaporator temperature gradient gets lower when said compressor is deactivated and said gradient is positive. 
     
     
       15. A control arrangement according to claim 13, wherein said switch-on hysteresis gets larger as the negative evaporator temperature gradient gets lower when said compressor is activated.